BEARDSLEY: POPULATION DYNAMICS OF ATLANTIC ALBACORE 



FISHING EFFORT (MILLIONS OF HOOKS) 



Figure 11. — Linear relation between catch per unit of 

 effort (CPUE) and effort (upper panel) and theoretical 

 equilibrium yield curves (lower panel) predicted for the 

 South Atlantic albacore longline fishery. The effort fig- 

 ures in the upper panel are means of the current year's 

 effort and the two preceding year's effort. Effort figures 

 in the lower panel are actual yearly values. 



When the data are combined from areas C, D, 

 and E, a decline in CPUE is evident to about 

 1963 (Figure 11). This decline is primarily in 

 area C. From 1963 to 1968 a steady increase 

 in CPUE is evident which represents the de- 

 crease in effort in area C and the increase in 

 effort in area D where excellent catches were 

 being made. It appears from the overall pic- 

 ture of CPUE versus effort that the albacore 

 population in the South Atlantic has declined 

 only slightly in relative abundance as a result 

 of longline fishing. 



This may be misleading. I suggested (Beards- 

 ley, 1969) that the small albacore in area D 

 formed the recruitment to the South Atlantic 

 population. This hypothesis was based on size 

 differences between the two areas; albacore from 

 area D were small, often averaging as little as 



10 to 12 kg, while those caught in area C usually 

 averaged 18 to 20 kg or larger. The monthly 

 distribution of catch rates also indicated seasonal 

 movement between the two areas. 



Eecent size information obtained from alba- 

 core landed in Puerto Rico and caught in area E 

 show that small albacore are a large part of the 

 catch. Recruitment to the South Atlantic pop- 

 ulation may take place in this area. Koto's sug- 

 gestion that small albacore move between the 

 Indian and South Atlantic Oceans lends support 

 to this hypothesis. The small albacore in area D 

 may well be transients in the South Atlantic, 

 and any population analysis would have to treat 

 them as a separate stock. 



Until the problem of stock identification in the 

 South Atlantic is resolved, any estimates of yield 

 are to be considered tentative. Consistently high 

 CPUE values in area D over the past 5 years 

 suggest that even greater yields are possible from 

 this area. The pronounced decline in CPUE in 

 area C demonstrates a significant response of the 

 population to heavy longline fishing pressure, 

 and any large increase in fishing effort probably 

 would not result in a significant increase in yield. 



POPULATION ESTIMATES 



I obtained the approximate average number 

 of albacore caught from each age-class in the 

 Bay of Biscay from 1963 through 1968 in the 

 following manner. 



Each length-frequency sample from the Bay 

 of Biscay (Figure 2) was separated into age- 

 groups in the same manner as described earlier. 

 The number of albacore in each age-group was 

 then divided by the total number of fish in the 

 respective sample to obtain the percentage con- 

 tribution of each age-group to the sample. This 

 percentage was considered as being representa- 

 tive of the contribution of that age-group to the 

 total catch for that year. An average percentage 

 contribution over the 4 years, 1967-70, was then 

 calculated for each age-group (Table 2). 



I then calculated the total weight of a cohort 

 of 1000 albacore using weights at age (Figure 5) 

 and average percentages obtained above (Table 

 3). The average annual catch from the Bay of 



853 



